1. Field of the Invention
The invention relates to the mixing of gases and liquids. More particularly, it relates to the dissolving and/or reacting of oxygen and other gases in liquids.
2. Description of the Prior Art
A wide variety of techniques and systems are known in the art for achieving the mixing of gases and liquids. One commonly used system comprises a stirred-tank reactor (STR) system in which, e.g., air is sparged into a reactor equipment with a mechanical stirring device. The impellers of the stirring device serve to mix the contents of the reactor so as to cause, for example, oxygen from air to dissolve in a body of liquid in the reactor vessel. Such STR systems can be used for a variety of gas-liquid mixing operations, e.g., large aerobic fermentations, such as are used to produce yeast or certain pharmaceuticals, or large leach tank operations, such as are used to dissolve gold from ore with an aqueous solution of sodium cyanide. In many such operations, however, it is desirable to add more oxygen or other gas than the conventional STR system is capable of efficiently dissolving or otherwise processing. As a result, other gas-liquid mixing processes and apparatus are needed to satisfactorily meet the practical requirements of various commercial operations. In many cases, however, it is desirable not to change the primary mixer system, but to add a secondary dissolution-process vessel to the primary mixer system.
A gas-liquid mixing system which is often used to augment the gas dissolution capabilities of a primary dissolver such as the STR is the so-called Side-Stream Pumping (SSP) pipeline contactor system. In the operation of the SSP system, liquid is typically recirculated from a primary supply source, such as the STR, through a recirculation pipe for gas addition at an elevated flow pressure and at a flow velocity sufficiently high to provide turbulent mixing conditions within the liquid. Such turbulent flow conditions are typically sufficient to disperse gas added to the liquid and, together with the use of elevated flow pressures, to enhance such dispersion for gas dissolution purposes, and, where applicable, enhanced reaction of gas and liquid or the constituents thereof. The liquid from the SSP system, containing high concentrations of said added gas, is then returned to the primary source to supply the desired enrichment thereof. While SSP systems are effective for gas-liquid mixing purposes, the pumping energy requirements of such systems are generally quite high, and this factor creates a major drawback to the use of such systems, particularly when substantial quantities of gas are to be dissolved in a liquid. The gas utilization of the SSP system, in addition, is often not as great as desired in practical commercial operations.
It will be appreciated, therefore, that a genuine desire exists in the art for a alternative means of dissolving large quantities of gas in, and/or reacting large quantities of gas with, liquids. Desirably such means would achieve the dissolving of gas in liquid with the expenditure of substantially less energy than is consumed in the use of SSP dissolver systems. In addition, such means would desirably enable high gas utilization efficiencies to be achieved as compared to such SSP systems. In particular, there is a desire in the art for such improved processing in applications where it is desired to efficiently disperse a separate gas, such as oxygen, in a liquid into which another gas, such as air, is being introduced.
It is an object of the invention, thereof, to provide an improved process and apparatus for the mixing of gases and liquids.
It is another object of the invention to provide an improved process and apparatus for the dissolving of gases in liquids at desirably low pumping energy requirements.
It is a further object of the invention to provide an improved process and apparatus for the dissolving of large quantities of gases in liquids at high levels of gas utilization combined with low pumping energy requirements.
It is a further object of the invention to provide an improved process and apparatus for the dispersion of a second gas into a body of liquid into which a first gas is being dispersed.
With these and other objects in mind, the invention is hereinafter described in detail, the novel features thereof being particularly pointed out in the appended claims.